Tower Kill

Our burgeoning network of towers for mobile phones, pagers, and digital television kills millions of migratory birds a year – and prevention may be as simple as changing a lightbulb

It’s
a rainy night in Georgia, and across the state line in northern
Florida. Under a low ceiling on this October evening in 1955, thousands
of neotropical migrant songbirds – warblers, thrushes, vireos,
tanagers, buntings – are moving south. They would be navigating by the
stars if the skies were clear, but with conditions like this they fall
back on their ability to sense the earth’s magnetic field. Normally
their flight plans would take them across the Gulf of Mexico, to the
Yucatan and beyond. Tonight, though, the final destination for many of
the birds lies just ahead: the 669-foot-high broadcasting tower of
station WCTV, on the Tall Timbers Plantation in the longleaf pine woods
outside Tallahassee.

As the first birds approach the tower, its steady red glow seems
to draw them in. Disoriented, they circle the structure like June bugs
around a porch light. They can’t break away. As more migrants join the
milling flock, birds begin to smack into the tower itself, the guy
wires that support it, and each other. Exhaustion overtakes them and
the collisions increase. An opportunistic screech owl, lured by the
migrant’s distress calls, snatches some of the casualties before they
hit the ground.

At dawn, the grass beneath the tower is littered with the small
corpses of the southbound travelers. A pickup truck pulls up, and
Herbert Stoddard begins to search the ground for whatever the predators
and scavengers have left. As he will every migration season for the
next 15 years, Stoddard inventories the night’s carnage. After his
death, others will continue the project for another 10 years.
Eventually, the toll will add up to 42,000 individual birds of 189
species.

Some incidents were worse than others. On one particularly bad
night early on in the study, the WCTV tower claimed 7000 birds. Large
kills were associated with overcast skies, north winds, and passing
cold fronts. The lunar cycle played a part, with more deaths occurring
during the dark of the moon.

The Tall Timbers chronicle and physician Charles Kemper’s 38-year
documentation of tower kills near Eau Claire, Wisconsin have given us
two of our best data sets on bird mortality at communications towers,
but beyond them it’s hard to quantify the losses precisely. Most of the
long-term studies have been in the eastern United States; there’s very
little data from outside North America. “The estimate is 4 to 5 million
deaths per year at the low end,” US Fish and Wildlife Service biologist
Al Manville says. “It could be as high as 40 to 50 million.”

As new technology – cell phones, high definition television –
drives a proliferation of towers, the toll, whatever it is now, is
likely to rise. Scientists are still trying to pin down what causes the
phenomenon, while environmentalists contend with a frustrating maze of
federal regulatory agencies.

Towers are just one hazard migrant birds face on their journeys to
and from their wintering grounds, and perhaps not the worst. Paul
Kerlinger, author of How Birds Migrate and columnist for Birder’s World,
provides some staggering estimates. Collisions with windows may kill
between 100 million and a billion birds each year, with electrical
transmission lines accounting for another 150 million and motor
vehicles 60 to 80 million. The annual loss to house cat predation may
exceed 100 million.

Still, the tower kills are troubling. Most of the victims are
passerines (songbirds) that migrate to the New World tropics, flying by
night to reduce the risk of predation. A much-publicized mass kill of
Lapland longspurs – prairie birds that winter in the Great Plains – in
Kansas in 1998 appears to have been an anomaly. “It’s a bizarre
misrepresentation of what occurs,” Kerlinger says. The longspurs
perished at a 420-foot-high tower in a January blizzard. But sodium
vapor lamps at a nearby natural gas pumping station may also have
attracted or disoriented the birds.

Neotropical migrants as a group have experienced declines due to
habitat loss and fragmentation on both breeding and wintering grounds,
and there is serious concern for such species as the cerulean warbler
and wood thrush. The American Bird Conservancy reports that 52 of the
230 North American species documented as tower casualties are on either
the Partners in Flight Watch List or the US Fish and Wildlife Service’s
(FWS) Nongame Birds of Management Concern List. One declining species,
the Tennessee warbler, is the third most common tower victim, after the
ovenbird and the red-eyed vireo. (Although the Conservancy’s report
mentions the endangered red-cockaded woodpecker, the two deaths cited
do not constitute a major mortality factor for this non-migratory bird).

We’ve known for years that birds are drawn to lighted structures.
“Folk who were in grief came to my wife like birds to a lighthouse,”
says Dr. Watson in Conan Doyle’s The Man with the Twisted Lip.
Mass deaths were recorded at electric light towers in Illinois as far
back as 1886; the first fatalities at a communications tower took place
at Baltimore in 1948. But scientists are only beginning to figure out
why illuminated communications towers are so dangerous.

Avian physiologist Robert Beason at the University of Louisiana at
Monroe has speculated that what attracts birds to lights is a
hard-wired escape response, a tendency to fly toward the brightest part
of the night sky. “Flying towards the moon would simply get the bird
above any fog or low-lying clouds and out of any potential problems,”
Beason explained at a Cornell workshop in 1999.

Seeing red
The color of the light and its duration (steady versus flashing or
strobing) seem significant. At a conference on Ecological Consequences
of Artificial Night Lighting in Los Angeles last February, Clemson
University ornithologist Sidney Gauthreaux described an unpublished
study from the late 1980s comparing migrant behavior near a tower with
white strobe lights, a tower with steady red lights, and a towerless
control area. The highest count of birds was near the red-lit tower,
where they showed a greater tendency to pause, hover, or circle than
birds passing the tower with the white strobes. Both towers were blown
down by a hurricane before the study could be repeated.

Why should red lights affect behavior more than white lights?
“Birds’ magnetic compasses seem to break down in red light,” Gauthreaux
told the Los Angeles conference. Bob Beason’s research points to a
linkage between birds’ sense of sight and the magnetoreceptors in their
brains. Other scientists had found that migratory species such as
Australian silvereyes and European robins become disoriented under red
light, losing their normal vectors. Where humans have three types of
color-sensitive cone cells in their retinas, birds have from four to
six types, including some that can sense ultraviolet light. Sensitivity
is greatest to long wavelengths in the red portion of the spectrum.
Beason’s work with bobolinks indicates the ophthalmic nerve carries
magnetic navigational information from the eye to the brain. So it
seems reasonable that red light could drown out the birds’ magnetic
sense, although the precise mechanism is still unclear. Under cloudy
skies, without astronomical cues to rely on, a faulty compass could
have fatal consequences.

Al Manville thinks the flash duration may also be critical in
pulling birds to a lighted tower. Preliminary studies suggest that the
longer the pause between blinks or flashes, the less the light attracts
birds.

How many agencies does it take to change a light bulb?
If the lights are in fact the problem, you would think it would be easy
enough to address. But this is where things become complicated, and
regulatory agencies with different constituencies and missions come
into conflict.

The Fish and Wildlife Service is legally mandated by the Migratory
Bird Treaty Act of 1918 to protect migratory birds, although it has
never sought prosecution of a communications company under the Act. But
it’s the Federal Aviation Administration (FAA), responsible for air
traffic safety, that prescribes how towers are lit, and the Federal
Communications Commission (FCC) that decides on their siting. The FAA
requires warning lights on all towers taller than 199 feet (the
European standard is about 350 feet). As of 2000, the FCC had over
46,000 such structures in its database. The proliferation of cell
phones and the Telecommunications Act of 1996, which requires that all
television stations transmit digital signals by 2003, have triggered
what Manville describes as “exponential growth” in new towers, many
taller than 1,000 feet.

The FCC, with no in-house expertise, has historically relied on
the communications industry to conduct environmental assessments for
proposed towers: “a classic case of the regulated community regulating
itself,” says John Talberth of the Forest Conservation Council.
(Earlier this year FCC announced plans to hire a “cultural resources
specialist” who will monitor industry compliance with environmental
laws.) Environmentalists’ attempts to influence the process have been
rebuffed. Last January the agency denied petitions by Talberth’s group
and Friends of the Earth objecting to applications for 29 towers,
holding that the two organizations lacked standing to intervene. The
two groups filed new challenges to three tower applications the
following month, the new wording emphasizing their members’ personal
stake in the outcome.

But another approach to the tower issue shows promise. Following
the 1999 Cornell workshop, a Communications Tower Working Group was
formed with Manville as chair, Beason in charge of research, and
Gauthreaux, Kerlinger, and other scientists participating. It’s an
alphabet soup of over 50 federal and state agencies, nongovernmental
organizations, and industry groups. In addition to F&WS, FAA, and
FCC, the Department of Defense, the Environmental Protection Agency,
and the Federal Highway Administration are involved.

Environmentalists are represented by the American Bird Conservancy, National Audubon Society, and Defenders of Wildlife.

One early product of the Working Group was a set of voluntary FWS
guidelines for tower structure and siting. These include using white
(preferably) or red strobe lights, keeping towers below the 200-foot
height at which lighting is mandatory, avoiding the use of guy wires,
clustering new towers within existing “antenna farms”, and locating
them away from significant bird habitat and migration corridors.

Manville says some companies have been very cooperative; American
Tower, for instance, consults FWS before deciding on sites. “Others are
still in denial,” he adds. And some federal agencies are taking
stronger steps: In three national forests in Arizona, cell phone
companies are being required to monitor bird mortality at the towers
they build, at their own expense.

Funding for basic research has been hard to come by. One promising
industry source dried up when Cingular took over Southwestern Bell. But
Manville says the National Fish and Wildlife Foundation has committed
up to $75,000 in matching funds for two studies. One would assess the
effects of lighting at a tower in Binghamton, New York. Researchers are
trying to negotiate FAA clearance to turn off the tower’s lights in
inclement weather, when no aircraft should be in the vicinity. Another
proposed study would use Global Information System technology to
determine where migrant birds rest and forage during the day. There’s
talk of restarting Herbert Stoddard’s work at Tall Timbers, where a new
tower is under construction.

“I’m hoping the industry will step forward,” says Manville,
mentioning interest from the Electric Power Research Institute in
underwriting research. He says Congress may also appropriate funds for
the US Geological Survey’s Biological Research Division, the research
arm of the Department of the Interior, targeting tower kill studies.

“We’re at a crux,” Manville sums up. “We’ve got some positive
things happening [ but] there are well over 120,000 towers out there,
and we don’t really know what these towers are doing to birds. We need
to get a good handle on what’s going on so we can effectively deal with
it.” Even if communications towers are not the greatest single threat
to birds, they’re a hazard we should be able to do something about.
With groups like the Fatal Light Awareness Program drawing attention to
the problem and further research in the works, the night skies may
become safer for the Western Hemisphere’s migrants.